The present invention relates to a cooling control system and a cooling control method for cooling an engine of, for example, a vehicle.
Conventionally, in a vehicle engine, a cooling circuit employing a radiator is used to remove excess heat from the engine, maintain a constant operating temperature, increase the temperature in a cold engine quickly, and heat the passenger compartment. The cooling circuit includes a coolant, which is typically a mixture of water and anti-freeze (such as ethylene glycol). The cooling circuit includes a water (i.e. coolant) pump that is powered via the crankshaft of the engine, usually through a pulley and belt assembly or gear set connected between the crankshaft and the pump, so its speed varies with the speed of the engine. The water pump is typically an impeller or centrifugal pump that forces coolant through the engine, hoses, radiator, and other system components. Also, when it is desirable to heat the passenger compartment, it pumps coolant through a heater core. When the engine is started cold, the coolant is below the optimum temperature for engine operation and it does not contain enough heat for transferring to the passenger compartment. In order to more quickly warm up such an engine system, then, a thermostat is used to restrict the flow of coolant to the radiator until the coolant is up to the desired temperature range. Once up to temperature, the coolant is routed through the radiator to assure that the temperature is maintained in the desirable range, and can be routed through the heater core to heat the passenger compartment.
One drawback to conventional water pump systems is that the flow rate of coolant is controlled by engine speed, not by the amount of cooling that the cooling system needs. Therefore, there is no way to optimize engine thermal management using a mechanical water pump alone. For example, when an automobile leaves a highway and enters city traffic, the engine speed and radiator cooling capability may not be adequate to cool the engine block in a timely manner. This could result in damage to vital engine components. Consequently, while this conventional type of cooling system is straight forward and relatively easy to implement, it is not very good at providing the optimum cooling for the particular engine and vehicle operating conditionsxe2x80x94particularly since the water pump is only a function of the engine speed, not any other factors important to maintaining the desired coolant temperature.
In order to improve the heat transfer efficiency of the radiator, these conventional types of systems also employ an engine fan, mounted adjacent to the radiator, to draw air through the radiator in order to better cool the coolant. The radiator fan is typically powered via the pulley driving the water pump or an electric motor. The pulley driven fan suffers from the same drawbacks as the pulley driven pump, while the motor driven fan, even though it operation is more flexible, adds to the electrical power load on the vehicle.
More recently, advanced engine cooling systems have been developed that will more precisely control the engine cooling. A more advanced system may be, for example, a system and method as described in U.S. Pat. No. 6,374,780, assigned to the assignee of this application, and incorporated herein by reference. These newer systems take into account additional factors that influence both what the desired coolant temperature is and how it is achieved. Such a system might include a radiator that receives the coolant flowing out of the engine, cools the coolant and returns it to the engine; a bypass circuit for making the coolant flowing out of the engine bypass the radiator when the coolant is below the desired temperature; a fan that is driven by a motor so that its speed can be controlled to be optimum for the particular engine and vehicle conditions (independent of the engine speed); an electronically controlled flow rate control valve (or valves) for regulating the percentage of coolant bypassing the radiator; and a water pump that is either conventionally driven via the crankshaft or by an electric motor, with the pumping rate of the electric motor controlled water pump precisely controlled to provide a desired coolant flow rate for the particular engine and vehicle operating conditions. Thus, the engine cooling system can be precisely controlled and the heating, ventilation and air conditioning (HVAC) performance optimized by controlling the coolant mass flow rate, the air mass flow rate, and the coolant flow path by one overall control strategy.
However, these advanced engine cooling systems have a drawback in that they require substantially more electric power consumption than the conventional systems. The electrically controlled valve, electrically controlled Water pump, and when employed, the electrically controlled fan all draw additional electrical power. Moreover, many additional electronic components are typically found on modern vehicles, which pushes the limit on the electrical current available from the vehicle charging system. This is particularly a concern with vehicle charging systems employing a conventional 12V electrical system rather than a high voltage system, such as 42 volts. And, in particular, pick-up trucks, sport utilities and other larger vehicles in the light vehicle class that run on 12 volts require more electrical power for the fan and water pump than typical passenger cars, so the current draw is even greater.
Thus, it is desirable to have an engine cooling system that overcomes the drawbacks of the conventional systems, while minimizing the additional electrical power needed to operate this system.
In its embodiments, the present invention contemplates a cooling system for controlling the temperature of an engine, with the engine having a rotating member. The cooling system includes a radiator, and an accessory drive adapted to be driven by the rotating member. The system also includes a pump clutch having an input member operatively engaging the accessory drive and an output member selectively engagable with the input member, and with the pump clutch electronically controllable to select the amount of engagement between the input member and the output member. A water pump is adapted to pump water through the engine and the radiator, with the water pump operatively engaging the output member to be driven thereby. Also, a controller operatively engages the pump clutch to thereby adjust the amount of engagement between the input member and the output member according to predetermined operating conditions.
The present invention further contemplates a method of cooling an engine, having a rotating member and a radiator, in a vehicle, the method comprising the steps of: driving an accessory drive with the rotating member; driving a water pump clutch input shaft with the accessory drive; monitoring predetermined engine and vehicle operating conditions; selectively changing the degree of engagement of a water pump clutch output shaft with the water pump input shaft based on the engine and vehicle operating conditions; and driving a water pumping mechanism with the water pump clutch output shaft.
An embodiment of the present invention provides a system that automatically adjusts the flow rate through the engine cooling system via a viscously clutched water pump driven off of the engine. The flow path can be adjusted via an electronically controlled flow control valve, and further thermal management can be obtained via an electronically controllable engine fan.
An advantage of the present invention is that a viscous clutched water pump reduces the electrical power draw from that of a motor driven pump, allowing an advanced engine cooling system to be employed without the need to greatly increase a vehicle charging system capacity.
Another advantage of the present invention is that the water pump speed can be controlled independent of the engine speed (below pulley speed).
An additional advantage of the present invention is that the pump clutch is configured so that the clutch fully engages if the power to the clutch is lost. This allows for a fail safe to ensure that engine damage due to overheating will not occur if electrical power to the pump clutch is lost.
Still another advantage of the present invention is that the overall efficiency of the clutched, engine driven water pump is higher than an electric motor driven pump due to the higher losses in conversion of mechanical energy into electrical energy by the vehicle alternator, and the conversion of electrical energy into mechanical energy by the electric water pump motor.